Chromatic Confocal System for Line-Scanning an Object

The invention relates to a chromatic confocal system for line-scanning an object. The invention relates particularly, but not exclusively, to a line-scanning 2D/3D imaging sensing system.

A line scanning sensing system is a known technology used for capturing images or data of a scanned object by scanning a single line at a time, rather than capturing an entire image of an object simultaneously. This technique is employed in both 2D and 3D sensing applications.

Line-scanning in 3D sensing systems typically uses a dispersion optical module to split the uniform white light into a continuous spectral line pattern at different heights. The spectrum of different heights reflected by the object surface, after been separated by a suitable grating, then focus on an image sensor to form an object profile image.

Most line scanning systems are designed to handle either 2D or 3D imaging primarily due to several technical and practical considerations such as sensor design, data processing, application requirements, cost and complexity, and performance optimization.

It is desirable to develop a line-scanning imaging system capable of both 2D and 3D sensing, which addresses image shadow issues, simplifies image alignment, measures deep holes and troughs effectively, and provides simultaneous 2D and 3D imaging capabilities.

Therefore, there is a need, among other things, to implement a novel chromatic confocal system for line-scanning an object.

An object of the invention is to mitigate or obviate to some degree one or more problems associated with chromatic confocal systems for line-scanning objects.

The above object is met by the combination of features of the main claims; the sub-claims disclose further advantageous embodiments of the invention.

Another object of the invention is to provide a novel chromatic confocal system for line-scanning an object.

A further object of the invention is to provide a method or an algorithm for generating a 2D or 3D image from image data received from an image sensor of the novel chromatic confocal system.

A yet further object of the invention is to provide a line-scanning imaging system capable of simultaneous 2D and 3D sensing.

One skilled in the art will derive from the following description other objects of the invention. Therefore, the foregoing statements of object are not exhaustive and serve merely to illustrate some of the many objects of the present invention.

In a first main aspect, the invention provides a chromatic confocal system for line-scanning an object. The system comprises a light module for providing a line-scanning light beam and a chromatic confocal lens module defining a first light pathway for directing the line-scanning light beam along said first light pathway and focusing the line-scanning light beam to impinge on a surface of the object. The lens module also defines a second light pathway for directing line-scanned light reflected from the surface of the object to one or more imaging modules. The line-scanning light beam has a predefined, limited range of wavelengths within the visible light spectrum.

Preferably, the predefined, limited range of wavelengths comprises blue and green light wavelengths within the visible light spectrum.

Preferably, the predefined, limited range of wavelengths comprises wavelengths in a range of 400 nm to 550 nm. Ine some embodiments, the predefined, limited range of wavelengths comprises wavelengths in a range of 450 nm to 550 nm.

Preferably, a numerical aperture of the first light pathway of the chromatic confocal lens module is configured such that the line-scanning light beam has a spot size diffraction limitation of about 0.5 μm, or less than or equal to 0.5 μm.

In a second main aspect, the invention provides a chromatic confocal lens module for a line-scanning system, comprising: an input for receiving a line-scanning light beam from a light source; a first light pathway for directing the line-scanning light beam along said first light pathway and focusing the line-scanning light beam to impinge on a surface of an object; a second light pathway for directing line-scanned light reflected from the surface of the object to an output; wherein the line-scanning light beam has a predefined, limited range of wavelengths.

In a third main aspect, the invention provides a method of generating a 2D or 3D image from image data received from an image sensor of the chromatic confocal system of the first main aspect, the method comprising: receiving Red-Green-Blue (RGB) image data from the image sensor; transforming the RGB image data to Hue-Saturation-Intensity (HSI) values; separating the H values from the HSI values; and using the separated H values to determine hue-to-displacement relationship values based on a plane mirror or plane gauge calibration model of the chromatic confocal system.

In a fourth main aspect, the invention provides a non-transitory computer-readable medium storing machine-readable instructions, wherein, when the machine-readable instructions are executed by a processor, they configure the processor to implement the method of the third main aspect of the invention.

The summary of the invention does not necessarily disclose all the features essential for defining the invention; the invention may reside in a sub-combination of the disclosed features.

The foregoing has outlined fairly broadly the features of the present invention in order that the detailed description of the invention which follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It will be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention.

The following description is of preferred embodiments by way of example only and without limitation to the combination of features necessary for carrying the invention into effect.

Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments, but not other embodiments.

It should be understood that the elements shown in the drawings may be implemented in various forms of hardware, software, or combinations thereof. These elements may be implemented in a combination of hardware and software on one or more appropriately programmed general-purpose devices, which may include a processor, memory, and input/output interfaces.

The present description illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope.

Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

Thus, for example, it will be appreciated by those skilled in the art that the block diagrams presented herein represent conceptual views of systems and devices embodying the principles of the invention.

The functions of the various elements shown in the figures may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (“DSP”) hardware, read-only memory (“ROM”) for storing software, random access memory (“RAM”), and non-volatile storage.

In the claims hereof, any element expressed as a means for performing a specified function is intended to encompass any way of performing that function including, for example, a) a combination of circuit elements that performs that function or b) software in any form, including, therefore, firmware, microcode, or the like, combined with appropriate circuitry for executing that software to perform the function. The invention as defined by such claims resides in the fact that the functionalities provided by the various recited means are combined and brought together in the manner which the claims call for. It is thus regarded that any means that can provide those functionalities are equivalent to those shown herein.

1 FIG. 2 FIG. 10 12 10 14 16 14 18 20 10 Referring to the drawings,provides an isotropic view andprovides a side-sectional view of an embodiment of a chromatic confocal systemfor line-scanning an objectin accordance with the invention. The chromatic confocal systemcomprises a light module, a chromatic confocal lens modulecoaxial with the light module, and one or more imaging modules,. The chromatic confocal systemmay be used to make 2D and 3D inspections of transparent materials, lens modules, electronic devices or components, computer chip wafers, light reflecting objects, or the like.

14 22 16 12 14 15 22 15 14 17 14 The light moduleis configured to provide a line-scanning light beam which passes along a first light pathwaydefined by the chromatic confocal lens moduleto impinge on a surface of the objectbeing line-scanned. The line-scanning light beam preferably exits the light modulevia a first slit deviceand enters the first light pathway. A slit of the slit deviceis preferably arranged horizontally with respect to the line-scanning light beam. The light modulemay include a heatsinkfor cooling the light module.

12 22 24 18 20 16 16 22 12 22 24 16 16 15 12 16 16 Line-scanned light reflected from the surface of the objectpasses back along a lower section of the first light pathwaybefore being diverted into a second light pathwaytowards the one or more imaging modules,. The chromatic confocal lens modulepreferably comprises sets of lensesA, B, C for directing and focusing the line-scanning light beam along the first light pathwayand for directing and focusing the line-scanned light reflected from the surface of the objectback along the lower section of the first light pathwayand then along the second light pathway. The sets of lensesA, B, C may comprise any suitable combination of: collimating lenses; chromatic lenses; and focusing lenses. Preferably, the chromatic confocal lens modulehas a magnification ratio of 1:1 from the first slit deviceto the object. The field of view (FOV) of the chromatic confocal lens moduleis ≥5 mm. The chromatic confocal lens module preferably comprises at least four pairs of lenses in the set of lensesB to produce a required amount of chromatic aberration.

14 The light moduleis configured such that it provides a line-scanning light beam which has a predefined, limited range of wavelengths within the visible light spectrum. Preferably, the predefined, limited range of wavelengths falls within a lower half of the visible light spectrum. Preferably also, the predefined, limited range of wavelengths comprises 40% or less of the light wavelengths comprising the visible light spectrum. In this context, the visible light spectrum is considered as comprising light wavelengths in the range of 380 nanometers (nm) to 750 nm. Preferably, the predefined, limited range of wavelengths comprise the blue and green light wavelengths within the visible light spectrum. In this embodiment, the predefined, limited range of wavelengths comprises wavelengths in a range of 400 nm to 550 nm, and preferably 450 nm to 550 nm.

14 16 22 16 The arrangement of the light moduleand the chromatic confocal lens moduleis such that a numerical aperture (NA) of the first light pathwayof the chromatic confocal lens moduleresults in the line-scanning light beam having a spot size diffraction (Abbe) limitation or focusing spot size of about 0.5 μm, preferably ≤0.5 μm.

3 FIG. 10 12 Reference is made towhich provides a graph showing intensity of different light wavelengths to their respective diffraction angles with the larger diffraction angles corresponding to the red and larger sized wavelengths and the smaller diffraction angles corresponding to the violet and smaller sized wavelengths. It will be understood that blue-green light has a smaller Airy disk than red-orange light and consequently blue-green light makes it possible to achieve higher image resolutions than light having larger wavelengths. Blue-green light can enable image resolutions of ≤0.5 μm to be achieved by the line-scanning light beam. This is resolution in image depth, i.e., resolution in the X/Z axis of the chromatic confocal systemwhere the X-axis aligns with the width of the line-scanning light beam, the Y-axis is aligned with the direction of scanning by the line-scanning light beam, and the Z-axis defines the depth of the imaged surface of the object.

10 In this embodiment of the chromatic confocal system, the spot size diffraction limitation (Abbe limitation) is given by:

where d is the diameter of the spot size; λ is the wavelength of light; and 16 NA is the numerical aperture of the chromatic confocal lens module.

10 In this embodiment of the chromatic confocal system, the spectral depth span of the line-scanning light beam is ≥1 mm for light wavelengths in the range of 450 nm to 550 nm.

18 20 18 20 18 20 12 24 The one or more imaging modules,may comprise a first imaging module comprising a 2D imaging moduleand a second imaging module comprising a 3D imaging module. The 2D and 3D imaging modules,are preferably arranged so as to receive line-scanned light reflected from the surface of the objectfrom the second light pathway.

18 20 12 24 Each of the 2D and 3D imaging modules,has respective means to extract line-scanned light reflected from the surface of the objectfrom the second light pathway.

26 16 12 22 24 12 24 16 28 28 28 12 28 30 30 A first beam splitter plateis provided in the chromatic confocal lens moduleto divert the line-scanned light reflected from the surface of the object, which initially passes back up the lower section of the first light pathway, into the second light pathway. The line-scanned light reflected from the surface of the objectpasses along the second light pathwayto exit the chromatic confocal lens modulepreferably via a second slit device. The second slit devicepreferably has a horizontally arranged slit. The second slit devicemay comprise a slit alignment or slit adjustment mechanism as will be described hereinafter. Line-scanned light reflected from the surface of the objectexiting from the second slit devicethen preferably passes through a collimating lens module. The collimating lens modulepreferably has a 25 mm focal length.

30 24 32 24 18 20 18 32 24 18 18 38 40 18 40 38 The collimated light emerging from the collimating lens modulethen passes further along the second light pathwaywhere it meets a second beam splitter platewhich diverts collimated light from the second light pathwayinto one of the imaging modules,; in this case, into the 2D imaging module. The second beam splitter platecomprises the means for extracting light from the second light pathwayinto the 2D imaging module. The 2D imaging modulepreferably has a condenser lens modulefor focusing the extracted light onto a first image sensorof the 2D imaging module. In this embodiment, the first image sensormay comprise a 5K-by-5K 2D image sensor comprising about 5000 pixels by 5000 pixels resulting in resolution similar to 4K or 1080p. The focal length of the condenser lens modulemay be 100 mm.

24 20 34 36 34 34 24 34 Collimating light passing yet further along the second light pathwayis then diverted into the 3D imaging moduleby a combination of a diffraction gratingand a prism or mirror. The diffraction gratingis arranged such that a plane of the diffraction gratingis normal to the second light pathway. In this embodiment, the diffraction gratingpreferably has a groove or line density of between 600 grooves or lines per mm (600 pl/mm) and 830 μl/mm.

36 34 36 24 24 12 20 42 20 24 12 42 20 The prism or mirrorfollows the diffraction grating. The prism or mirroris arranged such that its light reflecting surface is preferably placed at an angle of between 30 degrees to 40 degrees with respect to an axis of the second light pathway, i.e., with respect to a direction of collimated light travelling along the second light pathway. This angle range is selected as it beneficially places the 500 nm wavelength of light reflected from the objectnear to a center of the 3D imaging moduleand, more particularly, near to a center of a second image sensorof the 3D imaging module. More specifically, it is preferred that the light reflecting surface is placed at an angle of 37.08 degrees with respect to the axis of the second light pathwayto place the 500 nm wavelength of light reflected from the objectat the center of the second image sensorof the 3D imaging module.

20 44 42 20 44 38 18 44 20 38 18 44 20 42 40 The 3D imaging modulealso preferably has a condenser lens modulefor focusing the extracted light onto the second image sensorof the 3D imaging module. Again, in this embodiment, the focal length of the condenser lens modulemay be 100 mm. It is preferred that the focal length of the condenser lens moduleof the 2D imaging moduleis always the same as the focal length of the condenser lens moduleof the 3D imaging module. The condenser lens moduleof the 2D imaging moduleand the condenser lens moduleof the 3D imaging modulepreferably each have the same magnification ratios. These may comprise any of 4:1, 2:1, or 1:1. The second image sensormay comprise a 5K-by-5K 3D image sensor to provide the same image resolution as the first image sensor.

18 20 10 18 20 12 The arrangement of the 2D imaging moduleand the 3D imaging modulein the chromatic confocal systemis such that the two imaging modules,can simultaneously generate images from the same line-scanned light reflected from the surface of the object.

4 FIG. 2 FIG. 14 14 46 48 48 48 48 50 50 14 52 52 48 15 52 48 15 22 provides an exploded view of main components of the light module. The light modulecomprises a light sourcepreferably comprising one or more rows of light emitting diode (LED) chipscomprising an array of closely positioned LED chips. The LED chipsemit light in the blue-green light range of the visible light spectrum and preferably in the range of 400 nm to 550 nm. The LED chipsmay be arranged on a circuit boardto comprise a chip-on-board (COB) circuit board. The light moduleincludes a light guide rod. The light guide rodextends between the LED chipsand the slit of the slit device(). The light guide rodguides light emitted by the one or more rows of LED chipsto the slit of the slit deviceto inject said light into the first light pathway.

52 52 52 48 52 15 22 52 52 52 48 52 15 The light guide rodpreferably comprises a wedge-shaped rod or element with a substantially rectangular cross-section. The rodhas a light incident endA for receiving light from the LED chipsand a light emitting endB for transmitting light through the slit of the slit deviceto the first light pathway. The light incident endA is larger than the light emitting endB. The light incident endA is preferably of a size which closely or exactly matches a light emitting footprint of the one or more rows of LED chips. The light emitting endB is preferably of a size which closely or exactly matches the size of the slit of the slit device.

5 FIG. 48 provides a plan view of the array of LED chips(not to scale) with possible dimensions shown in mm although it will be understood that the dimensions shown are not essential dimensions of the array.

6 FIG. 6 FIG. 6 FIG. 6 FIG. 14 14 52 52 provides an optical simulation result of the light module. The image of the light moduleon the left ofshows the simulation of ray tracing. The upper image on the right ofcomprises the distribution of light intensity (or so called radiance), and the lower image on the right ofcomprises the distribution of blue and green colors at the light emitting endB of the light guide rod. It has been found that the uniformity can exceed 99%.

7 FIG. 1 2 FIGS.and 10 10 is a schematic sectional view of a 3D imaging module for the chromatic confocal systemof. Like numerals are used to denote like parts. In this embodiment of the chromatic confocal systemthere is no 2D imaging module, only a 3D imaging module.

10 18 20 18 20 1 2 FIGS.and 7 FIG. It will be understood that the chromatic confocal systemcan comprise: an embodiment with both the 2D imaging moduleand 3D imaging moduleas shown in; an embodiment with only the 2D imaging module; and an embodiment with only the 3D imaging moduleas shown in.

7 FIG. 36 24 24 also usefully illustrates the preferred angle of the reflecting surface of the prism or mirrorwith respect to the direction of travel of the image reflected light travelling along the second light pathway, i.e., with respect to the axis of the second light pathway.

12 42 20 40 18 12 40 18 42 20 40 42 18 20 1 2 FIGS.and As already explained, the preferred angle of 37.08 degrees or the preferred range of 30 degrees to 40 degrees angles are selected so as to place the 500 nm wavelength of light reflected from the objectat or near to the center of the second image sensorof the 3D imaging module. This is also the case for the first image sensorof the 2D imaging moduleof the embodiment of. Furthermore, the preferred angle of 37.08 degrees or the preferred range of 30 degrees to 40 degrees angles is selected so as to place the 450 nm wavelength and the 550 nm wavelength of light reflected from the objectnear to respective edges of the first image sensorof the 2D imaging moduleand near to the edges of the second image sensorof the 3D imaging module. This has the advantage that wavelengths of image reflected light residing outside the 450 nm to 550 nm range are substantially blocked from respectively reaching the first image sensoror the second image sensorby respective housings of the first imaging moduleand the second imaging module.

8 FIG. 7 FIG. 42 shows in grey scale the light intensities detected at different depths (Z) over the line-scanning width (X) and along the line-scanning length (Y) by the image sensorof the imaging module of, namely at depths corresponding respectively to 450 nm, 500 nm, and 550 nm.

9 FIG. 42 shows the width-wise (X) profile of each of the light intensities detected at different depths (Z) by the image sensor.

10 FIG. 42 shows (in grey scale) the light colours detected at different depths (Z) over the line-scanning width (X) and along the line-scanning length (Y) by the image sensor.

11 FIG. 1 2 FIGS.and 12 10 18 20 illustrates line-scanning a stepped objectusing the chromatic confocal systemofto enable simultaneous image generation by the 2D imaging moduleand the 3D imaging module.

12 FIG. 13 FIG. 14 FIG. 15 FIG. 12 12 12 12 shows in grey scale the 2D image spectrum color distribution of the stepped objectwhilstshows the 2D image intensity distribution of the stepped object.shows in grey scale the 3D depth image spectrum color distribution of the stepped objectwhilstshows the 3D depth image intensity distribution of the stepped object.

16 FIG. 1 2 FIGS.and 12 10 18 20 illustrates line scanning a trough objectusing the chromatic confocal systemofto enable simultaneous image generation by the 2D imaging moduleand the 3D imaging module.

17 FIG. 18 FIG. 19 FIG. 20 FIG. 12 12 12 12 shows in grey scale the 2D image spectrum color distribution of the trough objectwhilstshows the 2D image intensity distribution of the trough object.shows in grey scale the 3D depth image spectrum color distribution of the trough objectwhilstshows the 3D depth image intensity distribution of the trough object.

21 FIG. 1 2 FIGS.and 110 is a side sectional view of a 3D chromatic confocal systemfor line-scanning an object in accordance with another embodiment of the invention. Like numerals to those used in connection with the embodiment ofare employed but preceded by the numeral “1”. This embodiment is intended for only 3D imaging.

110 114 116 114 128 116 102 128 120 130 120 104 110 10 1 2 FIGS.and The chromatic confocal systemcomprises an illumination assembly or light module, a chromatic lens assembly or a confocal lens modulearranged coaxially with the light module, a slit alignment mechanismat a light output of the confocal lens module, a focusing mechanismassociated with the slit alignment mechanism, and an imaging lens assembly or 3D imaging module. Included is a collimating lens modulewhich forms part of the 3D imaging module. A 3D image sensor (not shown) is provided by a 3D camera. The operation of the chromatic confocal systemis generally the same as that described for the chromatic confocal systemofbut not including 2D imaging.

22 FIG. 114 110 117 148 152 148 115 106 152 114 provides a side sectional view and an exploded view of the light modulefor the 3D chromatic confocal system. The light module includes a heatsinkfor cooling the COB LED chips. A wedge-shaped light guide rodextends between the COB LED chipsand a slit device. A number of holdersare provided to position the light guide rodwithin the the light module.

23 FIG. 128 110 128 116 128 150 152 154 156 158 128 120 116 provides an isotropic view and an exploded view of a slit alignment or adjustment mechanismfor the 3D chromatic confocal system. The slit adjustment mechanismis preferably provided with 5 axis to enable adjustment of the slit positioned at the light exit or output of the confocal lens module. The slit adjustment mechanismcomprises an up/down axial adjuster, a first axial and tilt adjusterand a second axial and tilt adjuster. First and second plates,comprising a housing of the slit adjustment mechanismenable the 3D imaging moduleto be mounted to the confocal lens module.

128 24 24 The slit adjustable mechanismis preferably a multi-axis device being linearly adjustable in each of the Y and Z axis, rotatably adjustable around an axis of the second light pathway, and angularly adjustable with respect to the axis of the second light pathway.

24 FIG. 21 FIG. 120 provides side sectional views of two alternative 3D imaging modulesfor the 3D chromatic confocal system of.

25 FIG. 21 FIG. 26 FIG. 21 FIG. 110 120 110 shows light intensities with respect to depth, width wise profile, and light colors in grey scale with respect to depth of the line-scanning light beam of the 3D chromatic confocal lens moduleof.shows light colors in grey scale (left) and light intensities (right) at different line scanning depths detected by the imaging moduleof the the 3D chromatic confocal systemof.

27 FIG. 21 FIG. 28 FIG. 112 110 112 illustrates line scanning a trough objectusing the 3D chromatic confocal systemof.shows the 3D image spectrum color distribution and the 3D image intensity distribution of the trough object.

29 FIG. 21 FIG. 30 FIG. 112 110 112 illustrates line scanning a stepped objectusing the 3D chromatic confocal systemof.shows the 3D image spectrum color distribution and the 3D image intensity distribution of the stepped object.

31 FIG. 200 12 112 10 110 is a flow diagram of a methodor algorithm for line scanning an object,using a chromatic confocal system,in accordance with the invention.

200 60 160 10 110 62 62 162 60 160 2 FIG. 21 FIG. 2 FIG. 21 FIG. The methodmay be implemented by a processor() or() associated with the chromatic confocal system,executing machine-readable instructions stored on a non-transitory computer-readable mediumsuch as a memory() or(), the machine-readable instructions causing the processor,to implement the methods described herein.

A color sensitive camera or image sensor can achieve high color accuracy in Red-Green-Blue (RGB) space. 2D and 3D information can be detected in the optical slit by a single-color sensitive line camera. Displacement or depth of a translucent surface can be detected as a single dominant RGB color. The RGB color represents a specific wavelength which also represents a specific displacement or depth gamut and is a one-to-one relationship.

200 60 160 40 42 10 110 The methodconfigures the processor,to generate a 2D or 3D image from image data received from the image sensor,of the chromatic confocal system,.

200 200 The methodenables 2D and 3D sensing using a line-scan camera or image sensor instead of an area scan camera or image sensor with a possible speed up to 18K foot-per-second (fps). The methodcomprises a single algorithm which calculates the displacement or depth information and grey scale information of the surface of the line-scanned object instead of requiring two separate algorithms as in conventional chromatic confocal systems hence increasing the processing speed for image generation of the scanned object. The method also enables micron-level displacement resolution accuracy.

200 10 110 200 Whilst the methodis intended for use with the chromatic confocal system,using blue-green light, the methodcan be employed with white light and so is not limited to any defined range within the visible light spectrum.

202 40 42 204 The method comprises a first stepof receiving RGB image or pixel data from the image sensor,. A next stepcomprises transforming the RGB image data to Hue-Saturation-Intensity (HSI) values. Color can be transformed from the RGB color space to HSI values. Hue (H) is monotonic and a H value can be mapped to a specific wavelength. Hue is a color attribute which is invariant of surface roughness and lighting reflection characteristics. The RGB color space, once normalized to the range [0, 1], can be transformed to HSI values using the following equations:

Steps to be followed:

206 200 In a next step, the methodcomprises extracting or separating the separating the H values from the HSI values.

208 200 210 In a next but optional step, the methodcomprises comparing the I or S values corresponding to the extracted or separated H values to a predetermined or calculated threshold and optionally discarding any H values not meeting the threshold as missing pixels in step. The threshold may be determined or calculated from the corresponding I values and S values.

212 200 10 100 In a next step, the methodcomprises using the extracted or separated H values to determine hue-to-displacement (depth) relationship values based on a plane mirror or plane gauge calibration model of the chromatic confocal system,. Preferably, the calibration model comprises a polynomial function derived from a best polynomial fit of the H values obtained from the plane mirror or plane gauge calibration procedure.

214 200 216 12 112 In a next step, the methodcollects the depth data and in a final steppost-processes the depth data to generate 2D or 3D images of the scanned object,.

32 FIG. 300 10 100 300 300 is a flow diagram of a calibration methodor algorithm for the chromatic confocal system,. The methodmay be implemented using a high-precision linear Z-axis motor and a plane mirror or plane gauge as a reference flat surface. The methodinvolves calculating the flat surface profile's hue information to generate contour lines of the flat surface.

300 300 The methodincludes moving the Z-axis from low to high positions in linear steps throughout the measurement range. In addition to calculating the reference flat surface profile's hue information, it includes recording the hue information in each height position and recording the height positions from the Z-axis motor readings. The methodinvolves using a polynomial fitting model to model the hue-displacement relationship of the reference flat surface. The resulting regression polynomial model is saved for hue-displacement calibration.

300 302 10 100 304 300 10 100 10 100 306 10 100 308 310 312 308 310 314 316 The methodcomprises a first steparranging a plane mirror or plane gauge for line-scanning by the chromatic confocal system,. In a second step, the methodcomprises moving the optical probe of the chromatic confocal system,to a far end of the measuring range of the chromatic confocal system,. In a next step, the optical probe is moved in set distance increments to a near end of the measuring range of the chromatic confocal system,. The set distance increments could be set as 2.5 μm. In a next step, line spectral RGB image for the current set distance of the plane mirror or plane gauge reference flat surface is obtained. In a further step, hue information of the acquired line spectral RGB image for the current set distance is calculated. The method may include stepwhere, if it is determined that the optical probe has already been moved to the near end of the measuring range, the method does not repeat stepsandfor any further set incremental distances. Once all hue information for all acquired line spectral RGB images has been calculated in step, the method concludes in stepwith using the polynomial fitting model to model the hue-displacement relationship of the reference flat surface and outputting the calibration result.

33 FIG. 10 110 10 110 10 110 170 172 174 illustrates a calibration setup for the chromatic confocal system,in which the optical probeA,A of the chromatic confocal system,is arranged on a plateof the Z-axis motorabove the plane mirror or plane gauge.

The invention also provides a non-transitory computer-readable medium storing machine-readable instructions, wherein, when the machine-readable instructions are executed by a processor, they configure the processor to implement the method of any one of the appended method claims.

The apparatus described above may be implemented at least in part in software. Those skilled in the art will appreciate that the apparatus described above may be implemented at least in part using general purpose computer equipment or using bespoke equipment.

Here, aspects of the methods and apparatuses described herein can be executed on any apparatus comprising the communication system. Program aspects of the technology can be thought of as “products” or “articles of manufacture” typically in the form of executable code and/or associated data that is carried on or embodied in a type of machine-readable medium. “Storage” type media include any or all of the memory of the mobile stations, computers, processors or the like, or associated modules thereof, such as various semiconductor memories, tape drives, disk drives, and the like, which may provide storage at any time for the software programming. All or portions of the software may at times be communicated through the Internet or various other telecommunications networks. Such communications, for example, may enable loading of the software from one computer or processor into another computer or processor. Thus, another type of media that may bear the software elements includes optical, electrical, and electromagnetic waves, such as used across physical interfaces between local devices, through wired and optical landline networks and over various air-links. The physical elements that carry such waves, such as wired or wireless links, optical links, or the like, also may be considered as media bearing the software. As used herein, unless restricted to tangible non-transitory “storage” media, terms such as computer or machine “readable medium” refer to any medium that participates in providing instructions to a processor for execution.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only exemplary embodiments have been shown and described and do not limit the scope of the invention in any manner. It can be appreciated that any of the features described herein may be used with any embodiment. The illustrative embodiments are not exclusive of each other or of other embodiments not recited herein. Accordingly, the invention also provides embodiments that comprise combinations of one or more of the illustrative embodiments described above. Modifications and variations of the invention as herein set forth can be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated by the appended claims.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e., to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art.